In photography, there is a recognized need for providing flash illumination at an angle that is suited to the scene coverage angle of a zoom lens. The photographic zoom lens capable of a range of focus from telephoto to wide angle settings and provides the best image quality when the flash illumination angle is adjusted to correspond to the scene coverage angle. At a telephoto setting, for example, the optimum flash illumination is substantially well collimated. At its other extreme, a wide angle setting, the preferred flash illumination also has a relatively wide angle.
A number of methods for providing flash illumination at adjustable angles have been proposed. Conventional approaches vary the spatial relationship of the flash light source relative to the supporting illumination optics. For example, one way to change the scene coverage angle of the flash is to move the flash lamp along the optical axis of the flash reflector. As the lamp is moved away from the back of the reflector, the pattern of light is spread to cover a larger area. A disadvantage to this method is that the flash lamp must be moved mechanically. If the movement mechanism allows the flash lamp to move off-axis with respect to the optical axis of the reflector, then the pattern of illumination also shifts as a function of the location of the flash lamp with respect to the reflector.
Yet another method for changing the scene coverage angle is to position a lens at a variable position in front of the reflector along its optical axis. This approach is used, for example, to provide a variable strobe illumination angle, as disclosed in U.S. Pat. No. 6,598,986 and U.S. Patent Application Publication No. 2004/0037549 (both by Yano). This method can be effective, but requires that there be sufficient clearance in front of the reflector in order for the lens to travel along its optical axis. In addition, a mechanism for supporting and moving the lens is required.
Similar approaches using variable lens positioning include the use of retracting cylindrical lens arrays that can be suitably positioned according to camera focus, as disclosed in U.S. Patent Application Publication No. 2002/0009297 (Tanabe). Yet another technique adapts flash illumination angle by varying the relationship of a pair of wave lenses, as disclosed in commonly-assigned U.S. Pat. No. 5,666,564 (Albrecht). While these and related methods have merit for adapting the flash illumination angle for many applications, they require at least some level of mechanical movement and may not be easily adaptable, particularly for compact cameras. Solutions such as that disclosed in U.S. Pat. No. 6,278,845 (Terada), in which components in the finder optics path also serve to provide variable angle flash illumination, can be specifically tailored to individual camera designs, but are not easily implemented in a broad range of camera types.
A still further method changes the scene coverage angle of a flash by changing the shape of the reflector. Depending on how much angular change is needed, the volume of the reflector may change substantially. This provides an opportunity to vary the distribution of light within the scene coverage angle in addition to changing the scene coverage angle itself. While this can be a useful feature, it may require a complex mechanism that is somewhat sensitive and is not easy to operate.
While conventional solutions can provide some measure of variable flash illumination angle, there is felt to be considerable room for improvement. The need for a zoom flash mechanism that is relatively inexpensive and mechanically robust is particularly compelling with the advent of less expensive compact cameras, both digital and film-based.